The present invention is directed to a toe cap for reinforcing safety shoes, boots and the like. More particularly, the present invention is directed to a toe cap having increased tensile and compressive strength as well as improved impact resistance.
Originally, toe caps were made of metals such as steel. These caps necessarily made the shoes in which the were used heavy to wear producing increased fatigue in the wearer. When subjected to high compressive loads, steel toe caps would be permanently deformed and, in addition to possibly aggravating an injury to the wearer""s foot by complicating shoe removal, the toe cap and, hence, the safety shoe, would be essentially damaged to the point of needing replacement. In addition, steel toe caps are electrically and thermally conductive making them unsuitable for certain applications. Lastly, steel is magnetically interactive rendering shoes equipped with steel toe caps unsuitable for uses including certain military applications, and the like.
More recently, toe caps have been made from various plastic materials, typically fiber reinforced thermoplastic injection molding compounds. Any reinforced shoe must pass a rigorous set of tests established by the American National Standards Institute (ANSI), currently enumerated in ANSI Z41-1999, as well as a variety of other international tests for shoes/boots to be sold into those markets. Very few plastics are tough enough to pass muster with all of these standards. Frequently, because of material limitations, the thickness of the toe cap must be increased to provide the required tensile and compressive strengths and the necessary impact resistance. This increased thickness increases weight and the increased size may necessitate enlargement of the shoe envelope if the increased wall thickness takes up too much room in the shoe.
It is an object of the present invention to provide a toe cap which satisfies the compression and impact tests of the ANSI and standards of other foreign countries with a single comparatively thin design. The toe cap of the present invention is a reinforcement member having a generally C-shaped lateral cross section, said reinforcement member being made of thermoset structural composite material with a tensile strength of at least 30,000 psi, a tensile modulus of at least 2.5xc3x97106 psi, a compression strength of at least 35,800 psi, a specific gravity of at least 1.85, and a Barcol hardness of at least 65. More preferably, the toe cap is made of a material having a tensile strength of at least 50,000 psi, a tensile modulus of at least 3.8xc3x97106 psi, a compression strength of at least 42,000 psi, a specific gravity of at least 1.90, and a Barcol hardness of at least 70. A suitable family of materials is a thermoset vinyl ester based sheet molding compound reinforced with glass fiber and/or carbon fiber. The sheet molding compound has fiber content of about 63% and a typical fiber length in the range between xc2xd and two inches. The maximum wall thickness of the upper portion of the toe cap, including the top portion and the side walls, is in the range of between 0.100 inch and 0.250 inch. With a slight thickening of the wall adjacent the inner edge, the toe cap of the present invention is able to pass the impact testing and to be in compliance with all necessary standards without unduly increasing the weight or the envelope required to house the toe cap.
Various other features, advantages and characteristics of the present invention will become apparent to one of ordinary skill in the art after a reading of the following specification.